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Why Does My Shower Water Pressure Drop When the Toilet Flushes

Troubleshooting from George Brazil

So you’re enjoying your morning shower when you hear the toilet flush. You cringe because you know what’s coming next: a drop in water pressure followed by a short blast of slightly hotter water.

It’s nothing dramatic, of course. You still have enough water to keep showering and in 30 seconds everything returns to normal. But it’s annoying.

If your shower water pressure temporarily weakens every time the toilet flushes, the problem is most likely that you have a pressure-balancing shower mixing valve.

Not sure what that even means? Don’t worry.

We’ll explain what a pressure-balancing valve is, how it affects your shower water pressure and what you can do to improve your morning showers.

Why a pressure-balancing valve causes a drop in water pressure

A pressure-balancing shower mixing valve has one job: to control the temperature of your shower water.

But here’s the twist: pressure-balancing valves don’t actually read the temperature, instead they control the temperature indirectly by adjusting the ratio of hot to cold water pressure.

An example of how this works: You’re showering and decide you want a hotter shower. When you turn the lever, your pressure-balancing valve restricts the amount of cold water flowing into your shower and increases the amount of hot water pouring in. The result? A rise in water temperature.


Now, back to the toilet flushing…

A toilet requires a large amount of cold water to flush. So, when the toilet flushes while you’re in the shower, it’s stealing from your shower’s cold water supply. When the pressure-balancing valve senses the drop in cold water pressure, it responds by restricting the hot water pressure.

The result is a short period where you get slightly hotter water followed by a noticeable drop in water pressure until the toilet bowl fills back up.

The solution? Switch to a thermostatic valve

Believe it or not, you have options when it comes to shower mixing valves!

So if you’re tired of the unwelcomed changes in water pressure and temperature, we suggest switching to a thermostatic valve.


Well, a thermostatic valve can precisely control the temperature of your shower. With this valve, you’ll have two handles:

  • One for controlling water pressure
  • One for controlling the temperature

Thermostatic valves have tiny sensors inside them that respond directly to temperature so it’s constantly maintaining your shower temperature down to the degree without any changes in water pressure.

And the best part? Because they have two handles, it takes the guesswork out of finding the perfect shower temperature every time. Instead, just find the sweet spot and never adjust the handle again.

Want to install a thermostatic shower mixing valve?

If you’re ready to make the switch, you can use this video as a guide to your DIY installation.

Installing a thermostatic shower mixing valve will most likely involve cutting into the wall to access your shower plumbing. If that sounds like too much of a hassle, and you live in the Phoenix area, we’re here to help.

Just contact us today to get a quote on the install job. We’ll respond right away so you can enjoy better showers as soon as possible!

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